1. **Thaw Pastry:** Remove the puff pastry from the freezer and let it thaw on the counter for about 40 minutes. It should be pliable enough to unfold without cracking, but still cold to the touch. (If it gets too warm/sticky, pop it in the fridge).

2. **Preheat:** Preheat your oven to 400°F (200°C). Line two large baking sheets with parchment paper.

3. **Prep Chocolate:** If using chocolate bars, chop them into long, thin strips (batons) or ½-inch chunks. You want the chocolate to span the width of the croissant.

4. **Cut Dough:** Unfold one sheet of pastry onto a lightly floured surface. Use a rolling pin to gently smooth out the seams. Cut the sheet into 4 equal rectangles (or 6 for smaller pastries).

5. **Fill & Roll:** Place a row of chocolate along the short edge of a rectangle, leaving about ½ inch of space. Roll the dough over the chocolate once to enclose it. Place a *second* row of chocolate next to the roll, and continue rolling up the rest of the dough. (Traditional Pain au Chocolat has two sticks of chocolate inside!). Place the croissant seam-side down on the baking sheet.

6. **Repeat:** Repeat with the remaining dough and chocolate, spacing them 2 inches apart on the baking sheet.

7. **Egg Wash:** Whisk the egg and water together. Brush the tops of the croissants generously with the egg wash. This gives them that signature glossy, golden-brown shine.

8. **Bake:** Bake for 20–25 minutes, or until the pastries are puffed high and deep golden brown.

9. **Serve:** Let them cool on the pan for 10 minutes to allow the chocolate to set slightly. Dust with powdered sugar and serve warm.